A few thoughts.
It's great that your property manager provided multiple quotes. Did you have to ask for that, or was it required as part of the contract (e.g. for projects over a certain value, PM needs to obtain multiple bids)? If your PM obtained multiple bids for you automatically, without being required to, and without charging you extra for such, that's a plus.
Often times the roofer will provide a warranty also for workmanship. I have seen 5 years and 10 years on that. That roofer warranty I would care about, assuming that the company checks out as a reputable one that will be around then.
I am guessing the quotes are probably not identical, so hard to compare in summary. For example, what materials are they using - are they the same brand and grade and type of shingles? what about the underlayment? Does it include the dumpster and dumping fees? what about "Extras" like drip edges, etc?
Does your PM charge a % of the project value as coordination fee? If so, there may be financial interest so harder for your PM to say to choose one or the other $15K or $35K quote.
If it were me, I would ask the PM for which one he/she recommends. However, I would likely also do some due diligence on the companies, and then call 1-2 of them to ask them to explain what's included in the quote. It takes time and effort, but to me $15K-$35K is a lot of money, and a roof badly installed can lead to lots of problems. Luck.
