16 should be fine, but to future proof and if the budget permits it go for 32gigs. Clock speed upwards of 2800MHz, 3000. Also, DDR4 !! ;)
Might need to set the RAM speed to the advertised value, many start at 2133 (I think, have to check) out of the box. But that's a straightforward BIOS change, many guides on that online :-)