If you have seen in the video and you got MMM 15 as you said, so it should be there. I got MMM 16 Premium and if Easy mode is turned off I can see
To open synthesizer I click on Synthesizer and all available synth can be seen.
How does your MMM 15 works?
It would be much easier if you could attach screen shot.
Check my MMM 16 Premium screen shot To enlarge image click on it.
Additional information: for elastic audio put some audio on arranger then right click and choose elastic audio from menu or put some audion on arranger click on it and on Keyboard Press "S". If you do not know how to use elastic audio pleae ask ok.
The other user also told you Revolta2 is included in MMM 16 Premium.
It is not possible that you only deleted Revolta2 as it is in the Program Folder of Magix. Are you sure you often open your Program Files? If you have tried re installing you could check as follows if you got Revolta2 folder or not?
Open Magix, on Keyboard click "Y" key then click on Folder tab, Add Vst plugin path and you can browse synth folder and see if you got Revolta2 if you do click on it and click OK. If in your version you do not got this Add Vst plugin path, you will have to locate your Program Data(or else) which is some time a hidden file How to locate?
Click your normal C drive where Program folder is, click on TOOLS/Folder Options/View/ click radio button round one, Show all folders then click OK you could see all files, Program Data/ MagixMusic Maker/Synth in this folder you will find all synth. Do not forget to hide your files once again.
How you could get it back?
If you had purchased Box version or download and retain those installing CD/DVD or download link in that case installation from CD/DVD will be easier however, from download link as it is older version may be difficult.
But you can ask Magix support if you can provide them proof of purchase may be they can help you. You will need, Date of Purchase, Order Number(in cases of download product)