It may be worth a shot, it was likely never tested for 16gb as 8gb modules would have been well in excess of $2000 each back in 2010 if they were even available (they were $1700 or so in mid 2011 when i picked up my 2011 15").
I believe someone here with a similar vintage mini(?) who fitted 16gb and it worked. The mini of similar age likely has a similar chipset, which will be the limiting factor.
I suspect if it can handle >8GB (e.g., 10 or 12 with a 4+8 or 2+8 setup), it will handle 16. Yes mis-matched ram will be slower, but an 8GB dimm is what... 45 bucks now?
Worth a try if you ask me. If 10-12gb works (mis-matched), buy the other 8gb dimm for another 45 bucks so you have a matched pair, totalling 16 GB. If it doesn't work, sell the DIMM to someone else or just wear the $45 bet you made that didn't pay off.