Samsung 75 inch TV Wall Mount Screw Lebgth..........................

It's hard to answer without seeing both. Although 5mm doesn't seem like a lot, you have to remember that most of the force is sheer stress (assuming you're not mounting it on the ceiling). Assuming it's 4 bolts, 5mm is probably the minimum to get enough hold traction. I would use light finger strength only to wind the bolts into the back of the tv and mark them just shy of maximum depth. Most brackets come with spacer rings that either go between the tv and the bracket, or the bracket and the bolt head (they're usually hard black plastic), that let you adjust the depth the bolt goes to. See if you can find a combo that suits If all else fails, take a bolt with you to your local hardware supplier (so you can match the diameter) and buy the length you want.

I think much will depend on the actual TV. If TV has hole depth to accommodate 13mm, then getting a bolt that goes in 10mm would be sufficient and make any excess gap up between the TV and bracket using either the supplied spacers and or suitable sized metal washers.