Is this in the image what you mean ogden? I was hurrying up
About CMOS logic gates thanks for the idea Zero999, I didn't know they exist with dual voltage supply, are they accurate when giving those voltages? Because from what I remember they just have to keep values into their input ranges. But why did you put different resistances (39k and 100k) ? Maybe I didn't mention but I want my threshold voltages also to be ±2.5V so I would put those resistances equal, maybe both 39k.
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Maybe I got you, we need like 2/3 Vcc to make it switch so they can't be equal. Feedback one should be smaller. But I feel like these type of thresholds aren't precise.
CMOS logic gates will happily work from a dual rail, as long as the total supply voltage is within the voltage rating, so for ±2.5V, you need a part rated for 5V, which isn't difficult, the 74HC04 will do. The second gate could be five in parallel for reduced output impedance or, if you want to save space, there are dual gate parts such as the 74HC2G04.
I chose those values of R1 & R2 so the input voltage at the gate doesn't exceed the ±2.5V supply rails.
Why are you worried about the threshold voltages? As long as the rise/fall times of the 15V waveform are fast, compared to the frequency, the threshold voltages are unimportant.