3 walks a day? That's not very much activity for a Dachshund - and also might not be enough for her to be relieving herself. Your pup may be bothering you to go for a walk because she needs to pee. This breed is high energy, and even though they are small they need a good amount of stimulation. Expecting your dog to hold it from 7pm until 7am is unreasonable, at 15 months old she probably can't comfortably do that. You might try going for a walk right before you go to sleep, and then again first thing in the morning.
Have you gone through basic obedience training? If not, start there. Learning basic commands like sit and down will provide a good amount of mental stimulation and then you can go on to teach her increasingly difficult commands and tricks. You could even get her into a tracking or agility class after she masters the basics. Dachshund's were bred to hunt, and she might enjoy this. Talk to your trainer after she's close to mastering the basics and they can point you in the right direction. Since you mentioned it's very hot where you live right now, which I assume means you can't let her play outside much, working on obedience can take the place of some physical exercise.
Depending on where you live there is likely a dog daycare nearby - you could try enrolling her a few days each week so she has other dogs to play with. She will come home tired, and will not bother you to play as much. Along the same vein, do you have any neighbors or friends with dogs that you could set up a play date with? If not, there are free dog play groups in many neighborhoods, you just have to look. Check out Meetup.com, your local Petco, etc.
As far as toys and chews go, have you tried a stuffed Kong? You can get whatever size is appropriate for your pup and stuff it with whatever she loves (peanut butter mixed with kibble, cooked meat and greek yogurt, even just whatever you feed her for regular meals). Kong makes all sorts of durable, stuffable chew toys that are fantastic for keeping dogs occupied. You can also give the Himalayan Dog Chew a try - it should take your pup a while to chew it up.
At the end of the day the problem is that your dog is not getting the mental and physical stimulation it requires. A dog is not a fun toy for you to play with when you feel like it, it's a living creature that requires your time, love, and attention.