NEXT GEN VERSION HERE: https://www.nexusmods.com/witcher3/mods/7479

This mod is intended for those who believe that it makes no sense to have half of the Skellige quests' levels set lower than 16 when this is the suggested level for Destination: Skellige, quests where there is a bigger level difference from a chronologically earlier quest were changed as well and where it made sense to me. I also increased the levels in reward.xml, so you should earn full XP if you're not 5+ levels above the newly changed suggested levels. Fistfights weren’t changed because they aren’t affected by ±5 level difference.
Note: With the exception of Berengar’s Blade and Rough Neighborhood, I didn’t change levels for enemies to accommodate for the increased levels of the quests that I changed. You don’t get that much XP from killing enemies, but it takes a lot of time to find and change all the parameters in all of these quests for enemies and IMHO it’s not really worth the time. You can always turn on Enemy Scaling for a challenge, so I hope you won’t mind that.

List of changed quests (number in brackets is the original level and the number behind the new level):

• Novigrad Dreaming (7): 10
• Haunted House (7): 10
• A Favor for Radovid (9): 12 (actually set to lvl 12, but not in the journal)
• Missing Persons (15): 18
• Nameless (14): 18
• Blood on the Battlefield (20): 24 (actually set to lvl 24, but not in the journal)
• Through Time and Space (26): 28
• Skjall's Grave (28): 30
• Honor Among Thieves (9): 12)
• Rough Neighborhood (10): 26
• The Gangs of Novigrad (9): 12
• Berengar’s Blade (27): 19 (The Isle of Mists is the cut-off point, now in line with Ugly Baby)
• Stranger in a Strange Land (14): 17
• An Unpaid Debt (15): 18
• A Hallowed Horn (12): 17
• Flesh for Sale (12): 17
• Following the Thread (11): 17 (you get to Skellige after level 16)
• Free Spirit (13): 16
• From a Land Far, Far Away (13): 16
• Master of the Arena (14): 17
• The Cave of Dreams (14): 17
• The Nithing (14): 17
• The Price of Honor (14): 17
• The Family Blade (15): 18
• In Wolf’s Clothing (15): 18
• A Bard's Beloved (15): 18
• Armed Assault (15): 18
• For Fame and Glory (15): 18
• The Last Wish (15): 18
• *NEW* Black Pearl (13): 16 (Please note: check the section Conflicts for new info)
  

*IMPORTANT UPDATE*
Because of my stupidity, I've introduced a bug with this mod. It prevented you from obtaining A Miraculous Guide to Gwent and Zoltan gwent card from the scholar in the inn in White Orchard in the beginning of the game. This should be now fixed, so please download the new file to fix this issue. Sorry for the inconvenience. Special thanks to Arkwulf for identifying this bug. Thanks!

Conflicts:
If you have the Witcher Book Collection mod installed, you’ll have 4 conflicts, which cannot be resolved automatically with Script Merger. You have to use the line from the Witcher Book Collection mod AND you’ll have to change the parameter “level=11” to “level=14” otherwise this fix won’t work when you kill the katakan in the sewers during Now or Never. Then, you have to change the parameter “level=12” to “level=17” for mq2001_holmstein_completed, “level=15” to “level=18” for mq2001_kaer_trolde_completed and "level=13" to "level=16" for mq3031_2_finished_quest and then save.

Installation:
Simply put the mod folder in your Witcher 3 directory/mods. If this is your first mod, then just create a new folder called "mods" and put it in there. Mod Manager will probably work too. To uninstall, simply delete the mod. Resolve any other potential conflicts with Script Merger.

Enjoy!