How to increase the marching speed of APC?

Yes, you can research:

Suspension System (3rd line down)

Under

Vehicle Training

There are a few ways to speed up APC's such as the research items but only to a certain extent.

Using all vehicles in the formation will make the biggest difference. The Parts from the parts factory can help but have some restrictions on use, the explosion proof type is a trailblazer set part and has a buff for march speed but only when marching to gather. Other sets have parts that improve speed but only when the formations are a specific type of troops.

In some types of march you can use speed up items (once you have unlocked their use through research). Using speed ups can be stacked and will give the biggest boost to sped but are one time use only for each march.