Im stuck on 3 campaign missions for T55A

I`ve come back to the game about 2 months ago. After completing a few missions from the first campaign i am stuck on those 3 missions for T55A: LT-15 , MT-15 and SPG-15

Basically I only need to complete one of them in order to get the T55A because i can do the other ones with campaign orders.

Can you guys give me tips on how to do them?

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LT-15:

Best tank I have to complete it is my AMX 13 90. I got pretty close once with a combined of about 6500 but it is very rare to have a match like this.

MT-15:

Tried it in my Centurion AX but I dont know how I should do 2.5k damage to TDs. Especially if there are only 2 or 3 in the enemy team.

SPG-15:

Well… id like to avoid doing that since it is very hard to do. Not the assistance damage, but the part where I have to be top of the team by experience. I got the M53/55 which should work good for this mission. But playing arty is frustrating