What is this mod?:
I never liked the fact that followers level up along with the player. It makes the choice of followers less important and makes it so that someone like Uthgerd, who you just need to win a brawl with, is at roughly the same power level as someone like Mjoll, who you need to delve into a falmer-infested dwemer ruin and defeat a dwarven centurion in order to recruit. Static Follower Levels edits followers so that they no longer level with the player and have a static strength level appropriate for their profession, lore, and the amount of effort it takes to recruit them. It also makes follower choice more relevant in a deleveled Skyrim (i.e. Morrowloot Ultimate or Requiem). Side mission characters who only follow you briefly are also affected.

This mod does not run any scripts. It only contains edits to NPC records.

Their stats and skill levels are what they would have been at the chosen level. 

Compatible with everything as long as they dont script follower levels. I use this with NFF and it works fine. 

This mod requires a new game for the effects to take place!

Level Edits and Explanations:
If you don't like any of these edits, simply open the mod in xEdit and change/delete the records. Or you can make a recommendation in the comments and I might change it if it makes sense.
All housecarls - 15
All hirelings/mercs - 20
Ahtar - 15
Rikke - 25
Esbern - 30
Mjoll - 30
Cosnach - 15
Delphine - 25
Sven - 10
Faendal - 10
Benor - 15
Annekke - 15
Enmon - 10
Ghorbash - 20
Avulstein GrayMane - 15
Derkeethus - 10
Roggi - 10
Adelaisa - 20
Galmar - 30
Dark Brotherhood Initiates - 15
Eola - 20 - (Orcs were levelled to 20 just to make sure they don't die too quickly in the giant fights outside their stronghold)
Borgakh - 20
Ugor - 20
Lob - 20
Ogol - 20
Golldir - 15
Farkas - 20 (Non-circle Companions < Farkas < Vilkas = Aela)
Vilkas - 25
Aela - 25
Athis - 15
Ria - 15
Njada Stonearm - 15
Torvar - 15
Mercer Frey - 50 (A challenging boss fight to end the thieves guild quest. Mercer Frey has been acquiring limitless wealth so his power level reflects this)
Brynjolf - 30
Karliah - 30
Kharjo - 25
Barbas - 30
Onmund - 15 (College of Winterhold apprentices = 15)
Jzargo - 15
Brelyna - 15
Tolfdir - 30
Thorald GrayMane - 15
Veezara - 15
Nazir - 25
Maurice Jondrelle - 6
Erandur - 30 (A high-level follower for completing a daedric questline)
Aranea Ienith - 25
Orthorn - 15
Ralof - 15
Hadvar - 15
Malborn - 10
Chief Yamarz - 25
Valdr - 15
Illia - 25
Erik the Slayer - 15 (Different from other hirelings because lore-wise, Erik has no prior adventuring experience)
Uthgerd - 15
Vigilance - 15
Cicero - 40
Vidrald - 10
Meeko - 15
Stray Dog - 10
Serana - 30
Katria - 15
Ingjard - 20
Durak - 20
Celann - 20
Bran - 15
Neloth - 30
Frea - 25
Ralis Sedarys - 25 (High levelled as a reward for finishing such a tedious questline; even if profession-wise doesn't make sense)
Bujold - 25