I think the B1G could easily go to 15 if they know they have a 16th lined up for later. Have UConn play 8 football games instead of 9 to make the scheduling work, give UConn an automatic loss as far as determing eligibility for bowls or conference championship. Once deregulation has passed, it's no problem.
If you know who #16 is and know you want UConn, the sooner you get started the sooner you build market share in the critical New England/New York markets. If UConn increases the value of the next TV contract, and we probably do (certainly do if Fox is the bidder because they also get 51% of BTN revenue which we'll strongly increase), they'll want to get it done before they finalize the TV deal.
This temporary 15-only arrangement seems to me the most likely deal, between the GoR and the network entanglements I don't think a suitable 16 can be found in time, barring a B12 dissolution. But at next TV contract musical chair game, there should be a number of valuable applicants.