The Heavy Sniper is a high damage, slow reloading weapon.
When I have used this in-game, i have not found it to be very strong unless you use are using it for instant wall replaces. If you and your duo are carrying the sniper, one person can snipe the wall, then after they shoot, one person can shoot for the head of someone in the box to guarentee damage on healing players.
The long reload time is a great way to counter this weapon. If your opponent is using this to replace a wall, try to predict them and hold the wall. This will make them have to reload, and since this takes so long, you can keep pressuring them to make sure they never get a chance.