Yo, some quick feedback for you.
This map is rather overscaled, all the areas feel far too large and empty, and overall the map is incredibly flat and uninteresting, rarely with any cover.
The path the payload takes stays on the same level pretty much throughout the whole map until you reach the end section, there is very little fun involved in pushing a cart down very long, flat hallways to be honest. The overall flatness and linearity becomes an even bigger issue when you consider sight lines for snipers as well as wrangled sentries. There are several incredibly long sightlines that stretch over vast areas of the map, a good sniper or 2 could shut down the routes completely. (some images below). I would look at some decompiled valve maps and compare gameplay space sizes to your map, and also look at how alternate routes and cover work in them.
Another issue is the fact you can get on top of literally every building as any class, this seems to be intentional as you've added ramps but it gives those above an overwhelming advantage over everybody else. If the entirety of RED set up on the building above BLU Spawn at the start, there is very little BLU could do to counter it. I'd tone down the access to those rooftops and if you do scale the map down make sure you either lower the roof level, or make it obvious which roofs you can sit on. The way height advantage is often dealt with is to limit access to health and ammo up there, so the position doesn't confer an advantage forever.
Image dump with comments below:
Building below is BLU Spawn, all the rooftop is available for RED to sit and spam from. All routes from Spawn off to the first checkpoint seem liable to be shut down by sentries and spam via small doorways.
Massive sightline across the first checkpoint area, a good sniper can shut down the cart pushers easily.
2nd checkpoint area is still very flat with little cover available.
Another large sightline from RED Spawn to 3rd checkpoint.
Last area is again mostly flat, and BLU have to push the cart forever right in front of RED Spawn, they would either have to spawncamp RED or be prepared for a horrendous time pushing the cart past it.
Another big issue with the map is that the map hasn't been separated into smaller areas with skybox brushes. This is awful for optimisation, and it also means a sticky jumper demo can literally fly all the way across the map in one go and snipers can easily pick people off from the other side of the map.
This is a good guide on scale in maps:
https://tf2maps.net/threads/guide-scale-and-your-map.12605/
Here's a handy list of tutorials for mapping in general, there are some useful optimisation ones in there too, worth looking at I think:
https://tf2maps.net/threads/tf2-mapping-link-resources.22471/
EDIT: Found my favourite optimisation guide -
http://www.interlopers.net/optimization/index.php?chapter=intro it is a long read, but thoroughly recommended for anyone getting into source mapping.
That's all I've got at the moment, if you want any feedback on anything in particular let me know. Hope this helps a bit.