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[DdsLedg]

Hi,
Had some great advice from here in the past, and you guys are much better at this than me, so thought I'd reach out again. I've put a TL;DR at the bottom.

I'm the author of Midwood Isle and as part of the update I am planning. The mod has always had some issues with lag, so I'm looking for some advice. I think its related to the mod being an ESM.

I created the mod as an ESP in the LE CK, then turned it into an ESM using the ESMify script for xEdit.

Below is what I found when testing the FPS:

Spoiler

Admittedly I don't have the best PC, so for reference when loading the game up around the Falkreath region, the game runs at approx 60fps. After about 5 mins of exploring around Falkreath, I start getting lag spikes down to about 25-40fps.

Now, when I load into Midwood Isle, into the main city, as an ESM file, it runs at about 45-55fps, and also immediately has quite frequent lag spikes which can be down to 20fps.
The base fps doesnt seem to vary much depending on where I'm looking.
Weirdly enough, toggling the grass off with the console command "tg" also doesnt make any difference (if anything it makes the spikes slightly worse).
Additionally, I tried deleting all the trees within a few cells (but worth mentioning not the LOD) and this doesnt seem to make a difference to the base fps, but does reduce the amount of spikes somewhat.
I also tested putting up huge plane markers, but this doesnt really reduce the base fps or the spikes (unless you stand and stare at the marker).
As part of the update, I tried putting up occlusion planes in the city inside buildings, and removed a few of the misc items, but when comparing the old file to the new one, there isn't really any difference in fps despite the new changes.
When moving out of the city, the fps is around 40, and drops down to 20fps fairly regularly. I think this occurs when the game loads the next cell.

Now the weird thing is, if I was to not convert it to an esm, and instead load up the city with the mod being an esp, the base fps is around 55-60.
Exploring out of the city makes no difference either - the fps is still 60fps and there are no lag spikes.
The lag spikes only really start about 5 mins after playing (similarly to if I went into regular Skyrim). Before its been running a while, they just dont happen.
Another thing to mention, is that for some reason the navmesh seems to just work better as an esp. For some reason the city NPCs just stand around a bit more when the mod is an ESM. No clue why this is happening either, as they can and do move still, just not as much.

I think the reduced fps and lag spikes are due to the mod being an esm. The only reason I can think of is that (to my knowledge) an esp loads everything as persistent, whereas an esm has everything temporary and loads it in as you see it. That should in theory cause it to run faster, (so no idea why its slower) but it could explain the lag whilst exploring (loading the new cells).
Regardless, I have no idea how to prevent this. With the mod being as big as it is, as well as issues like the grass and sky bug which affect esp files, I'd like to have the mod run smoothly as an esm, but I can't think how.
I'd appreciate any advice

TL;DR - Converting Midwood Isle to esm with the ESMify script seems to cause a lower fps and frequent lag spikes when compared to leaving it as an esp. No idea why this is