Definitely boards exams come first. Agar tumhare pcm Mein 75% marks na ayein, toh jee mains Accha rank aa v Gaya toh kya fayeda. Otherwise, if you can manage both at the same time, then you can do. But board exams first. Mains aap nxt yr de sakte hoon, but brd exams bar bar nehein Ata.
But jee mains ka thoda sa preparation karlo,, ncert agr acche padha & solve kiya Hua hein toh vo board exams k sath sath mains Mein v Kam ayein ga & upar se thoda mains ka jo shortcut methods hota hein physics, maths k liye vo thoda padhke Jana. Bas,, but boards first!!
Best of luck for your exams...