FROM: TMG Exchange 2010 -> TO: F5 Exch 2010+2016 Coexistence - Poor Performance

which iApp did you use? there is no 2010 + 2016 one.

if your setup works for 2010 and 2016 together then you run the 2016 one and they will proxy towards the 2010 ones. dont put 2010 and 2016 servers in one pool.

where did you buy your F5? is there perhaps a F5 partner that can help?

or if you have a support contract try to involve F5 support, as long as follow the iApp guide they should be able to guide you.