Should I negotiate?

I have two offers in hand from Company A and Company B. I counter offered Company B with the offer from Company A (I have a bias to join Company A). Company B gave me 15% hike on the existing offer from Company A. The joining date of Company B is in 3 days while of Company A is in 5 days. The onboarding process of Company A is also started, like I have received the intimation for initiating the onboarding process. The gap between the two offers are not much. Is there any chance that Company A might rescend the offer instead of matching if I counter them?

Note: Company A is a medium sized MNC Company B is a medium sized fast paced startup.