BhG 2.15

syntax

he puruṣarṣabha (O bull among men!),
ete (these) [mātrā-sparśāḥ] (material sensations) yam (whom) sama-duḥkha-sukham (for whom pleasure and distress are equal) dhīram (the wise) puruṣam (person) na vyathayanti (they do not afflict),
saḥ hi (he indeed) amṛtatvāya (to immortality) kalpate (he is eligible).

grammar

yam	–	yat sn. 2n.1 m. – whom;
hi	–	av. – because, just, indeed, surely;
na	–	av. – not;
vyathayanti	–	√vyath (to tremble, to waver, to be agitated, to be afraid) Praes. caus. P 1v.3 – they cause to tremble, they affllict;
ete	–	etat sn. 1n.3 m. – these;
puruṣam	–	puruṣa 2n.1 m. – a person (from: √pur – to precede, to lead or √pṝ – to fill, to nourish, puru – abundance, pūru – people);
puruṣa-rṣabha	–	puruṣa-rṣabha 8n.1 m.; KD: puruṣo ṛṣabha iva – man as if a bull, the best of men (from: √pur – to precede, to lead or √pṝ – to fill, to nourish, puru – abundance, pūru – people; ṛṣabha – bull, the best of any kind); or TP: puruṣāṇām ṛṣabha iti – bull among men;
sama-duḥkha-sukham	–	sama-duḥkha-sukha 2n.1 m.; BV: yasya duḥkhaṁ ca sukhaṁ ca same stas tam – for whom pleasure and distress are equal (from: sama – the same, equal, equivalent; su – prefix: good, excellent, beautiful, virtuous; kha – cavity, hole, nave; su-kha – joy, happiness; dur / dus – prefix: difficult, bad, hard; duḥ-kha – pain, difficulty; literally: good or bad hole in the nave [of a wheel through which an axis runs] that makes the moving smooth or not; or from: su-√sthā and duḥ-√sthā);
dhīram	–	dhīra 2n.1 m. – steady, calm, sober, wise (from: √dhṛ – to hold or √dhā – to put);
saḥ	–	tat sn. 1n.1 m. – he;
amṛtatvāya	–	amṛtatva abst. 4n.1 n. – for immortality (from: √mṛ – to die; mṛta PP – dead, a-mṛta – not dead, eternal, nectar of immortality, amṛtatva – immortality, eternallity, liberation);
kalpate	–	√kḷp (to be fit for, to correspond, to be able) Praes. Ā 1v.1 – he is eligible;

textual variants

puruṣaṁ puruṣa-rṣabha → puruṣāḥ puruṣa-rṣabha (people, O bull among men);
sama-duḥkha-sukhaṁ → sama-sukhaṁ-duḥkha (equally treating pleasure and distress);
dhīraṁ → dhīrāḥ (they wise);
kalpate → kaṁpate (he trembles);

Śāṃkara

The key:
an excerpt from the commented verse
quotes from the scriptures
starting polemic

(Question): – What good will accrue to him who bears heat and cold and the like? (Answer): – Listen.		śītoṣṇādīn sahataḥ kiṃ syād iti śṛṇu –
That wise man whom, verily, these afflict not, O chief of men, to whom pleasure and pain are same, he for immortality is fit.		yaṃ hi na vyathayanty ete puruṣaṃ puruṣarṣabha | sama-duḥkha-sukhaṃ dhīraṃ so ’mṛtatvāya kalpate ||2.15||
That person to whom pleasure and pain are alike, – who neither exults in pleasure nor feels dejected in pain, – who is a man of wisdom, whom heat and cold and other things such as those mentioned above do not affect in virtue of his vision of the eternal Self, –		yaṃ hi puruṣaṃ same duḥkha-sukhe yasya taṃ sama-duḥkha-sukhaṃ sukha-duḥkha-prāptau harṣa-viṣāda-rahitaṃ dhīraṃ dhīmantaṃ na vyathayanti na cālayanti nityātma-darśanāt ete yathoktāḥ śītoṣṇādayaḥ |
that man, firm in his vision of the eternal Self and bearing calmly the pairs of opposites (such as heat and cold), is able to attain immortality (moksha).		sa nityātma-svarūpa-darśa-niṣṭho dvandva-sahiṣṇuḥ amṛtatvāya amṛta-bhāvāya mokṣāyety arthaḥ kalpate samartho bhavati ||2.15||

Rāmānuja

tat-kṣāntiḥ kim arthā ? ity ata āha—yaṃ hi iti | yaṃ puruṣaṃ dhairya-yuktam avarjanīya-duḥkhaṃ sukhavan manyamānam amṛtatva-sādhanatayā sva-varṇocitaṃ yuddhādi-karma anabhisaṃhita-phalaṃ kurvāṇaṃ tad-antargatāḥ śastra-pātādi-mṛdu-krūra-sparśā na vyathayanti sa eva amṛtatvaṃ sādhayati | na tvādṛśo duḥkhāsahiṣṇur ity arthaḥ | ata ātmanāṃ nityatvād etāvad atra kartavyam ity arthaḥ

Śrīdhara

tat-pratikāra-prayatnād api tat-sahanam evocitaṃ mahā-phalatvād ity āha yaṃ hīti | ete mātrā-sparśā yaṃ puruṣaṃ na vyathayanti nābhibhavanti | same duḥkha-sukhe sa tam | sa tair avikṣipyamāṇo dharma-jñāna-dvārā amṛtatvāya mokṣāya kalpate yogyo bhavati

Madhusūdana

commentary under the verse BhG 2.18

Viśvanātha

evaṃ vicāreṇa tat-tat-sahanābhyāse sati te viṣayānubhavāḥ kāle kila nāpi duḥkhayanti | yadi ca na duḥkhayanti, tadātma-muktiḥ sva-pratyāsannaivety āha yam iti | amṛtatvāya mokṣāya

Baladeva

dharmārtha-duḥkha-sahanābhyāsasyottaratra sukha-hetutvaṃ darśayann āha yaṃ hīti | ete mātrā-sparśāḥ priyāpriya-viṣayānubhāvā yaṃ dhīraṃ dhiyam īrayati dharmeṣv iti vyutpatter dharma-niṣṭhaṃ puruṣaṃ na vyathayanti sukha-duḥkha-mūrcchitaṃ na kurvanti so ‚mṛtatvāya muktaye kalpyate | na tu tādṛśo duḥkha-sukha-mūrcchita ity arthaḥ | uktam arthaṃ sphuṭayan puruṣaṃ viśinaṣṭi sameti | dharmānuṣṭhānasya kaṣṭa-sādhyatvād duḥkham anuṣaṅga-labdhaṃ sukhaṃ ca yasya samaṃ bhavati tābhyāṃ mukha-mlānitollāsa-rahitam ity arthaḥ