Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?  

RE: Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?

Yes it is possible to Combine Infill as long as the combined infill thickness does not exceed the Maximum layer height for the nozzle size. 

Typically a 0.4mm nozzle can print up to 0.32mm layer height, reliably. 
so if you are printing at 0.15mm layer height, you should be  able to combine infill every two layers to make the infill 0.3mm thick
If you are printing at 0.1mm you can combine every three layers, or every two layers
If you are printing at  0.7mm you should be able to combine every four layers, every three layers or every two layers 
if you are printing at 0.05mm I expect you could combine every six layers, or every five layers, every four layers,  every three layers, or every two layers  I have not had much luck printing at 0.05mm  with the Mk3 series printers  (the  Mk1 and Mk2 was fine, but that had a smaller hobbed gear in the extruder... )

note you need to be in advanced mode or expert mode to see this option

while you are there have a look at 'Only Infill Where needed. the slicer will estimate whether infill is required to support the top layers and will not infill, if it thinks support for the top layers is not required... 
be aware the slicer does not know if you intend to put pressure onto the model in the area where slicer doesn't add infill. so you need to be careful where you use the feature
regards Joan

RE: Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?

And if you mean external supports for the part rather than infill then support heights in PS are not tied to the printed layer height anyway by default. It changes automatically. It’s why layer count on the preview slider can differ to what expected when supports are enabled. 

RE: Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?

I'm not aware of a way to specify a layer height for supports. But I'd be very happy to stand corrected and learn a new trick. 

RE: Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?

Thank you, for the in depth answer!

I actually thought about external supports, but with internal I can also reduce my print time for sure. I did not know about the only infill when needed option before 😀

@Neophyl but how do I change it?

RE: Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?

Change support height ?  As far as I know you cant. It uses the highest layer height it can get away with generally, except when it comes to the interface layers and also when it approaches the layer its supporting.  For example if you set your contact z distance to 0.2 then it will adjust some layers to get where it needs to, to get the interface layer that far away/below your supported surface regardless of its position.  

There are a couple of things, it will use the min/max layer height as defined under your extruder settings in Printer Settings>Extruder>Layer Height Limits.  The other exception is when you have Synchronize with object layers enabled, however that particular settings is only available with a contact z distance of 0, ie when using soluble supports.

So there's really no need to have a setting for controlling support height to make printing quicker, it already does that by default.  You get far more time gains in other ways.  Like manually defining areas of support so there's less of it to print for example.

RE: Printing supportmaterial at 0,3mm layer height and the rest at 0,15mm?

Just checked it in the slicer, it really works automatic. Dont remember Cura and Simplify3D ever did this which I used before.