I2C weird data and clock output/input
Neither waveform looks at all normal for an SMBus transmission. In an ideal situation of transmitting the clock waveform during the transaction period should have an approximate 50% duty cycle.

I doubt that the pullup resistors are the issue but I would like to comment that trying to use resistors in the 15K to 20K range is very non conventional. Real world SMBus applications use pullup resistors in the range of 2.2K to 4.7K.

It will be hard to suggest further debug steps because I do not know how you are generating your traffic (SMBus IP block or bit-banged). Also unknown are factors such as MCU pin connections, pin configurations, any applied drivers or even level translators.