The normal settings for your Time Capsule wireless are already optimized for best performance, so unless you have changed some settings around, there is not much that you can do to improve performance....unless....you want to start over again and reset the Time Capsule back to default settings and then set it up again to see if will help the wireless.
Sometimes, it will help to assign separate names to the 2.4 GHz and 5 GHz signals, but I've not seen much improvement when I've tried this in the past.
Resetting the Time Capsule back to default settings and then setting it up again is something that you should do whenever you make a major change on a network, like changing the modem, or changing your Internet Service Provider. However, sometimes you can get away with not doing this.
If the Time Capsule seems to be working OK with your other devices, my recommendation would be to reset the Apple TV back to its original default settings and then set it up again. Once the Apple TV has been reset back to default settings, temporarily move the Apple TV close to the Time Capsule to set it up again.
Ideally, you would want to use a permanent wired Ethernet cable connection from the Time Capsule to the Apple TV, because that is always the fastest and most reliable type of connection to use.
If you cannot connect the Apple TV using a wired connection, keep in mind that any type of obstruction in the direct signal path between the Time Capsule and Apple TV will slow the wireless signal significantly, so you would want to have line-of-sight between the Time Capsule and Apple TV as much as possible.
If that is not possible, how far apart will the Time Capsule and Apple TV be located from each other?
How many obstructions.......walls, ceiling, heavy furniture, large mirrors, etc.....are there in the direct signal path between the Time Capsule and Apple TV?
Some forms of newer home construction use a type of wall and ceiling insulation that incorporates a metal foil backing on one or both sides of the insulating material.....and, as you already know.....not much of a wireless signal is going to make it through metal, so wireless can present a challenge as far as good performance is concerned.