No reason to go on I5 for anything. OP is in Visalia. Without question the route is 99 to 58 to 15 to Vegas. Per Google that is 360 miles. If you go over the Grapevine and pick up the 210 to 15 and up to Vegas the route is 445 miles plus you've added Los Angeles traffic to your trip.
Both routes require a fairly steep climb and a mountain pass. I think the Grapevine actually goes to a little higher elevation. Each pass can get snow, but it's fairly rare since neither is really that high. But both have closed to snow a couple of times this year. They mostly close because nobody carries chains on those routes.
You're not going until April, so snow will be more unlikely, but not out of the question. So just check the weather. Also plan your driving time as about a half a million people from Los Angeles go to Vegas every weekend. You won't hit that Los Angeles traffic until Barstow, but if you go at the wrong time on a Friday evening you can be at 20 mph all the way from Barstow to Vegas. And if you're coming back on Sunday, if you don't get out of Vegas by 10am at the latest, you run the risk of 20 mph all the way back to Barstow.