Any suggestions? It only takes about 15 min before the right hand starts to go numb and my fingers tingle. This never happened on my old Trek road bike.
I have had the bike for 350 miles and it is becoming more and more annoying.
I am no expert - however, I can tell you what helped me. I have two bikes - a traditional, fast road bike, and I also have a "hybrid" bike - very similar to a city bike. On the hybrid bike I upgraded to Ergon GP3 grips and that has really helped a lot.
Frequently change your hand position while riding (the Ergon GP3's will help you discover new hand positions). Sometimes I will securely hold onto the handlebar with one hand, straighten my back so it's almost vertical, and take my other hand off the grip - to give the other hand a rest. While riding like that (one hand securely on the grip, back almost vertical) I perform the following exercise (see image below) because your blood flow is getting blocked and this exercise can help with that. (no, I do not earn a living as an artist - ha)
I ride road bikes with drop bars and never get tingly hands falling asleep. You might try a bike fit, or discuss this problem with your bicycle mechanic. Numb/tingly hands is a common discussed bicycle fit problem if you do a google search.
I recently purchased a single speed electric bicycle that had flat bar mountain bike style handlebars, and rediscovered the single arm, hand position with the upright riding position my body has never liked.
I tried some wide Butterfly Trekking handle bars, they worked nicely with the brake levers I had to use with a Trip Wire to cut power to the motor when you braked, but the handlebar were too wide for my comfort level. I then was able to get Tektro RL340 Aero Brake Levers modified with a trip wire for a carbon fiber road bike drop bar style and all my neck, shoulder, and arm problems went away.
I have an REI 1992 XR touring bike that came with drop bars, and that has also become a trend for many gravel riders and a few downhill professionals with suspension forks. Might be something for you to try, to see if using that style handlebar, that provides many different arm and hand positions will let you avoid the numbness you are experiencing with the single arm/hand upright riding position.
I found the ebike flat bar Mountain Bike handlebar forced me to use a different body position that created problems, and right now it seems your body does not like that riding position...
Discuss the problem with your bicycle mechanic that would be the cheapest first step option...
There are many different things that could contribute to hands going numb. You went from drop bars to I assume a riser bar so body positioning has changed. Try moving your seat forward to bring you into a more upright position. Seatpost height, is it too high? Do you ride with a backpack or hydration pack? This will compress a nerve in your shoulder making your hands numb. I mix my rides up throughout the week. MTB, gravel, and road always riding with a backpack. I find that one hand goes numb consistently when on a road or gravel bike. Moving the strap alleviates this. Gloves....if you ride with them are they too tight? Without seeing how your setup is, one cannot diagnose the problem, but your first look is body positioning. You just need to tinker with everything and bring tools with you to make changes as you ride. Find the sweet spot and things will be golden.