Am playing on Death March since ~lvl 4 (although I started with Blood and Broken Bones - yeah, I know that won't give me the achievement at the end of the game, but that's not what I'm worried about).

Even though I have installed some mods to increase difficulty ... and since I'm someone who likes doing as many side quests as possible ... (am not the kind of person who enjoys rushing the main questline) ... I now find the main quests - after returning to them from side quests - too easy. The fix seems to be to install a "slower leveling" mod.

My question: Would you - at this stage (lvl 17, 1st Witcher 3 playthrough, currently at ~20% of the storyline with almost 100h spent) - reommend to restart the game?

The differences for this new playthrough would be (a) Death March difficulty from the very beginning, and (b) a "slower leveling mod" installed.

Thanks for any insight!

Instead of restarting you could try playing with enemy upscaling enabled. It's in "Options\Gameplay\Enemy upscaling". By default it's turned off.

Danke!