Anything preplaced (preloaded) in your map, in the World Editor (Units ,Structures, Doodads, Destructibles, Upgrades) increases load time, but not by much by themself.
Map Initialization triggers increase load time as well. Depends how much stuff you got there, usually it doesn't increase the loading by that much. Triggers/systems in the map header too.
Object Editor data too, if you have too many custom stuff, it will increase load time.
Playable map size also determines load time.
I would say the main cause to your 1.5 minutes is the 100-300 levels of abilities.
If you have heroes in your map preplaced in the world editor, it will preload all of those abilities during loading screen.
You could use triggers to spawn the heroes later in the game (not during map init).
This would decrease loading time but for each hero spawned, the game will freeze for a few seconds (only when a hero enters game for the very first time), thanks to your 300 levels of abilities that it has to load up.
I have a map with heroes that have 20 levels for each ability and I don't preload anything so map loads in 20 seconds. However once the heroes enter the map for the very first time, the game freezes for all players for 1 second because it had to load all of those ability levels. Nothing too big, Dota freezes for a second when players pick heroes too. I'm not sure how long the freeze would be with 300 ability levels though.