typically 147 recoil softer of differently at least. with 147 the recoil is more of a push and the sights tend to move more to the rear than upward. The slide tends to cycle slower with these type loads.
with 115s at minor power factor recoil tends to push the sights a little more upward than rearward. The slide also tends to cycle faster with these loads.
If both are loaded to the same power factor (which is a big deal in IDPA) the main difference i have noticed is the sight movement.
you could buy some of the federal champion that is sold at walmart. I have shot 1000s of that stuff and is it is great. Out of my pro i got it to shoot a little under 4 inch groups at 25 yards. The recoil is the softest of most factory 115 grain loads and is pretty clean. Another good thing i like about the federal is the primers arenice and soft so if you did any work to the striker you wont have any problems ignighting them, and they have great brass for when you do reload. I also used to use the Remingtion UMC 9 124 grain. The recil was nice but it was dirty and the velocity was to close to minor for my comfort. I did not shoot this ammo for accuracy.

147 recoils softer but slower than 115.

I personally like the snappiness of 115. I shoot the wwb from walmart and it has never given me problems. Heck I have used some wolf before just not as accurate as winchester.

The Federal Red Box is what I shoot ike most have already mentioned. It is the softest 9mm I've tried, and I get acceptable accuracy. If I was going for pure precision, the 124's are what my glocks like.

Carry ammo is another story.

I run whatever Walmart has on sale. Usually Federal, but I've run every brand they sell. Never noticed any difference on recoil. Faster follow ups aren't going to gain you much if anything. Most shooters lose time on sloppy reloads or not understanding the course of fire. Speed of follow ups is waaaaayyyyyy down the list.

I only shoot steel cased ammo in IDPA, cause im cheap and it doesnt give me any problems.

I'm not too experienced at this, but when I asked the same question elsewhere, I was pointed toward the Atlanta Arms & Ammo 147gr ammo. I've recently ordered some to try. Up until now my Sig P226 TacOps has seen nothing but about 3000 rounds of Federal Champion (Red Box) 9mm 115gr for competitoins and training. It will be interesting to see if I notice a difference. FWIW I ordered the I9147 reman stuff, not the "competition" stuff. Supposedly they are the exact same load, only in once-used brass.

No disrespect to some of the other posters - I have LOTS of room to improve my reloads, my course-reading, etc. And I'm sure that they're right - there is far more time in getting the skills down. I just like to remove all the excuses I can - and this is one more thing I can "upgrade" relatively inexpensively.

In the future I would look into a reloader / dillon

When I bought my Dillon my shooting improved because I could shoot more rds for less money
That and it help to have a range in the yard