Southern California - my legs are spent

okay im new to road biking ive really had a great time the last two weeks with my new hobby road biking,but my legs feel like jelly.i ride a mountain bike usually on the street for my cardio and im shocked that moving to a road bike could make my legs this sore.Let me share with all of you im learning the sram double click and i wad a in the wrong gears on big uphills that i had no business being on.i road flat 15 miles on friday and my legs are just tired.any advice on how to get my legs back or is it obvious i just need to rest.I had no idea how differently the legs react to a road bike as opposed to a mountain bike.should i raise or lower my seat?

I've always been told that mountain biking builds your strength, road biking builds your endurance. Test rode a bike with SRAM dubble-clickies. Took a bit of getting used to. Fit your bike the normal way- might take a bit of fiddling. Pivoting the seat downward by 1/2 inch and scooting it back by the same amount made a big difference.

As far as I can tell, you'll get faster and faster by the month but the legs will always be sore after a hard effort.

I don't think it'll be long before the easy efforts create no soreness. Maybe a couple weeks tops?

Let me share with all of you im learning the sram double click and i wad a in the wrong gears on big uphills that i had no business being on.any advice on how to get my legs back or is it obvious i just need to rest.

It sounds to me that it is obvious you just need to ride more on the road bike. And as far as being on a hill that you had no business being on, there is no such thing. Your on it, you ride it. Go down, start over again. The legs will come with time. Before you know it, it's GMR,Baldy, and Crystal Lake with no problems.:50:

If you haven't already you might look into getting a bike fitting to rule out poor fit. Some rest and more experience on the bike will take care of normal leg fatigue. Most likely you are just hitting your muscles at a slightly different spot than on the mtb. I know that I can do a brutal hike where I am limping around for a week after, but hop on the bike the next day and put in a hard effort with no soreness at all while pedaling. As soon as I get off the bike it's back to shuffling around like an old man. It is because I ride almost every day, but hike maybe twice a month. In my experience the soreness stops with regular use of the muscles. Doing back-to-back hard rides on the weekend, my legs might be tired on the second day, but they haven't been sore in a long time.

Another vote for a professional bike fitting.
I remember feeling like a doofus for paying Nate Loyal $180 to shift my saddle a few millimeters forward and up, and my cleats another few millimeters in some direction...
...but after a few weeks more of riding, I realized it was the best $180 I'd ever spent. It completely transformed my riding.

On top of that, road riding is fundamentally different from mountain biking. There are frequently times during a mountain bike ride where the rider must clench up and muscle-through situations. But on a road-ride, those brief, steep sections are much less frequent, and you spend a lot more of your time exerting maximum effort while focusing on remaining unclenched.
On your next road ride, instead of hammering through the whole thing, focus on breathing deeply, remaining relatively relaxed, and pedaling as smoothly (but powerfully) as you can.
Believe me, it's a lot harder than it sounds, and "remaining relaxed" doesn't mean you aren't busting @$$!
If you can master this tendency to clench up when riding hard, you will go much, much faster than you can currently ride.

best advice i could possibly get my legs feel better today and im just gonna have to ease into this 15 miles rides on the street seem so short to me but ill just have to do 10 miles and work back up till im in road bike shape