Which add ones are you talking about can you please be more specific and from where have you purchased them?
I bought through Adobe web page the following 2 addons that i want to use with Lightroom CC 2015
Vodoo for free and Presets against paiment.
Both appear on the "my add-ons page" as installed but they don't feed through my Creative Cloud app for Win10. I have checked if the file sync is active and yet it is. The folder for my files does't show any zip file.
Vodoo Lounge Preset is not compatible with LR CC 2015, please check the compatibility, would suggest you to check the same for others and the ones that are compatible try below mentioned steps -
Please make sure that file sync is on.
If file sync is on and they still do not install please try installing them using Extension manager, as mentioned in the option " Where to find it" in your purchased add ones.
https://creative.adobe.com/addons/products/2628#.VfQ4TRGqpBc (check this with all compatible add ones)
Thank you, the setup you're showing me it's what I have. I have a "stupid" question: do I need specific add-ons compatible with CC or 5.0 - 6.0 would be ok as well?
Yes you need specific add ones, as some of them will be compatible with 5.0 and some with 6.0/CC 2015