My wife loves drinking Moscato and Stella Rosa but they don't intoxicate her. I have to occasionally spike her drinks (obviously knowingly) with whiskey for her to feel a "buzz." Are there any wines that are maybe not as sweet as the 2 mentioned but less dry that provider maybe like a 12 to 15% alcohol content?
It depends on how sweet you are looking for. If you are looking for very sweet than dessert wines are the way to go, a Sauternes or Mustacel will be at least 12% if not higher. If all you want is a fruitier wine then many German white wines like Rieslings or Gewürztraminers tend to be on the sweet side, sometimes too sweet for many palates. Slightly less sweet whites are Sauvignon Blancs, Chenin blancs, soaves, the list goes on. All of these should be above 12%
Reds are tough for people with sweet palates, there are red dessert wines out there, and there are sweeter reds but there's no variety I can think of that is reliably sweeter. Roses are often sweet, especially the cheaper ones like White Zinfandel, but those can be low quality. A good Zinfandel red is a great wine, but not what I'd consider sweet.
Most fortified wines such as port, Madeira, (sweet) sherry, Commandaria are both very sweet and are very high in alcohol. Many are in the range of 20% ABV. I would strongly [pun intended] suggest seeing if she enjoys Port or Madeira. My personal favourite strong, sweet wine is Elysium Black muscat. It is so sweet that I commonly have it as dessert in restaurants.
A little primer on alcohol and sugar in wine. The lower the alcohol is usually associated with higher acid levels because the grapes are picked less ripe. Champagne is a good example of this. To offset the biting acids, winemakers usually add sugar to compensate. That's why so many low alcohol wines are sweet.
Can you find higher alcohol wines that are sweeter? Sure, dessert wines come to mind. Sauternes, Ice Wines, Tokay, Late Harvest wines are sweet with more alcohol. A lot of mainstream wine brands, like Sutter Home are purposely made sweeter. Unfortunately, the cheaper the wine, usually the sweeter it is.
Like I always mention here, wine is an adventure that only you can travel. You need to discover what you like (or your wife in this case). But I think these are several recommendations that should set you on the path.