395 through the Owens Valley is terrific! I highly recommend it if you have the time. The Alabama Hills near Whitney Portal is the site of many, many early westerns. You'd probably recognize the background. Take Whitney Portal Road from Lone Pine.
Manzanar is is a national historic site as the site of one of the WWII internment camps. It's famous from the book & movie "Farwell to Manzanar".
Mammoth Lakes is a beautiful place to stop. If you have more time, Devil's Postpile Nat'l Monument is a very interesting rock formation. Still, if you have limited time, I'd probably bypass that in favor of seeing the tufa formations at Mono Lake.
The June Lake loop is also a very scenic diversion. Oh, and don't forget Bodie, one of the best preserved ghost towns around. And as I said, just as you're about to leave 395, you definitely want to see Mono Lake near Lee Vining.
Once you get on 120 through the Yosemite high country, you're right, Tuolumne Meadows is a great place to stop and hike. And it's missed by 90% of Yosemite visitors. Then, as you continue toward the valley, you must, must stop at
Olmsted Point, which has the most amazing views down Tenaya Canyon all the way to Yosemite Valley, including terrific views of Cloud's Rest and Half Dome.
Other than that, I can only recommend about another half-dozen things to do. Nothing much to see, really
No, really, make a day of it (or longer), and enjoy yourself! It's a great trip!
-Bob
ETA - BTW, I agree with the PP, that it will take way longer. It should take lots longer, or you haven't stopped to see enough of the natural beauty! But you're right, traffic will be much less. The I-15 portion is just a little bit of the trip, and the most boring part. The fun starts once you get to the Owens Valley, past China Lake.