Welcome to the community!
First, thanks for posting clear pictures and uploading the 3MF file. This removes a lot of the guesswork from helping you.
Here are a few things I noticed between your photos and the 3MF file:
As uploaded, you may have noticed the message that you can’t use organic supports with variable layer height. However, your model doesn’t require supports in its current state, so you should be fine to disable that.
Here’s some suggestions, and I’ve re-uploaded the modified 3MF file:
head2 – modified.3mf (456.9 KB)
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Disable supports altogether, and instead, increase your wall count to 3. For angles this shallow, that should be enough.
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Experiment with setting the sparse infill density to 1% using rectilinear. Combined with the increased wall thickness, this should be enough, but you may need to try increasing the density to 2 or 3%. This should provide sufficient supports internal to the structure while saving internal nozzle movements and filament thus speed up the print while not sacrificing quality.
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You’re using the layer height tool incorrectly. Here’s what I mean: you set the entire model at a 0.20 layer height. However, the way you used the variable layer height tool essentially tries to smooth the whole model. This resulted in:
At the top, a layer height of 0.08 and at the bottom, a layer height of 0.14. This completely overrides all the other layer height settings so even if you set the layer height to 0.28 for the rest of the model, you aren’t getting any benefit. Please rmember, layer height is supposed to only be applied where you have refinements in curves or details, not so much on vertical walls.
Here’s what to do instead:
If you want to pick up speed, set the model to a 0.28 layer height and only use the variable layer height for the top of the curve. You may need to use the smoothing function to make the transition gradual.
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While I wasn’t able to match the exact time your original file showed, I was able to get it to 1h:18m using these methods.
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Other Possible Suggestions
After making the changes above, here are some other things to consider.
I’m noticing what appears to be a clear demarcation in layer changes. This might simply be due to the angle, but it could also be caused by incorrect temperatures or improper filament tuning.
Two factors can influence this: one is speed. Let’s not dive into using modifiers to correct speed here, as that’s a more advanced topic and will require trial and error. It’s typically only worth the effort if you plan on continually printing a model and want a fully dialed-in print.
On a more practical note, try running an overhang test from Printables. A temp tower using Orca Slicer would be better, but I don’t want to overwhelm this post with too many details. An overhang test is easier to interpret if you’re new.
Select a simple model from the list and print test models at different temperatures. At first, use wide variations to figure out if you should go higher or lower, then dial in from there. For generic PLA, start at 220°C and test at 190°C and 240°C to find the extremes.
Post processing
Sometimes you can only go so far. Then it comes to sanding and painting. Search for posts here on the optically clear topic last year for some tips if you’re really interested.
These suggestions above BTW are from a similar experience I had and and a lot of wasted filament. If any of these suggestions save you you some time, I will have done my good deed for the day. 
I had a project last year that I did that was the skull from hell.
Final print was 22 hours. 90+ hours over 2 months and 3 spools of filament figuring out how. 
This was a lot of trial end error.
This was a gift to my daughter-in-law upon her entrance into med school, her reaction was priceless. In the end, the results were worth it!!!
Here’s another one that is more similar to yours. In order to achieve the final smooth surface, I had to resort to post processing(sanding and painting) to achieve the smooth “resin-printer-like” finish. I’m afraid that sometimes, there are simply no shortcuts. 
