No, you can stay on Windows Vista, 7 or 8 or XP or previous if you want.
Microsoft is nagging us with pop-ups and little button in task bar to upgrade. There is no easy simple solution to block those messages. There are ways to stop them by removing an update or making a registry change which will work fine for geeks, but I would not suggest for the average Windows user.
For the average user you are just going to have to learn to ignore the messages. They are irritating as I see them everyday as I have not done those advanced methods.
Windows 10 is a free update thru next July and it can look similar to the desktop in Windows 8 with the tiles or look more like 7 with a menu although the menu is slightly different looking than Windows 7 and has some look of Windows 8. You may want to try it on someone’s computer and see how like and if you do then it is free to upgrade. You can probably play a tiny bit on displays in a store to get feel. People on Windows 8 should feel perfectly fine with Windows 10. People on Windows 7 will definitely like better than Windows 8.
If you want to try the advanced methods to block the messages go to https://support.microsoft.com/en-us/kb/3080351 and they show you the steps.