1. Use a distortion pedal. This is the most common way to add distortion to a guitar amp. Distortion pedals come in a variety of shapes and sizes, and each one has its own unique sound. Some popular distortion pedals for heavy music include the Boss DS-1, MXR Distortion +, and ProCo Rat.
2. Turn up the gain on your amp. The gain control on your amp controls how much distortion is produced. Turning up the gain will increase the amount of distortion, making your sound heavier. Be careful not to turn the gain up too high, as this can cause your sound to become muddy or harsh.
3. Use a booster pedal. A booster pedal can help to increase the signal from your guitar, which can make your amp sound heavier. Booster pedals come in a variety of shapes and sizes, and each one has its own unique sound. Some popular booster pedals for heavy music include the MXR Micro Amp, Boss GE-7, and TC Electronic Spark Booster.
4. Use a different speaker. The speaker in your amp plays a big role in how your amp sounds. A speaker with a higher wattage rating will produce more volume, while a speaker with a lower wattage rating will produce less volume. A speaker with a higher sensitivity rating will produce more sound for a given amount of power, while a speaker with a lower sensitivity rating will produce less sound for a given amount of power. A speaker with a larger cone size will produce more low end, while a speaker with a smaller cone size will produce more high end.
5. Change the tubes in your amp. The tubes in your amp play a big role in how your amp sounds. Different tubes have different characteristics, and some tubes are better suited for heavy music than others. Some popular tubes for heavy music include the 6L6, EL34, and KT88.
By following these tips, you can make your Fender Frontman 15G amp play heavy distortion. Experiment with different settings and pedals to find the sound that you're looking for.