Vacation time is very important to me since where I am living and will
be working is across the country from any of my family. Is it safe to
negotiate with company A so that I could have 15 days PTO even though
I am entry level?
You could ask for more time off, but be aware of how that may look to your potential employer.
You are an entry level worker. While time off may be important to you, your employer likely wants to hear how important work is to you, how you want to launch your career, how you want to learn and grow rapidly and the value you can add to their company.
Indicating that time away from work is of primary importance to you might be a red flag for some employers (it would be for me). It might make for a poor first impression.
You might have enough leverage to pull it off. The employer might want you to work for them so much that they are willing to change their PTO for an entry level employee. But I'm guessing that won't happen.
You might also consider asking for unpaid time off, if the time is really what is most important to you. When my company hired folks from a country half-way around the world, they typically took no time off the first year, carried it over to the second year, and then occasionally augmented that with unpaid time off. This made their trip home worthwhile and we considered that concession part of the price of hiring folks from that country.
But they never came in asking for that right away as a entry-level employee, in my experience.