question

Not quite sure what you're saying/asking.

MPPT will convert input voltage and current into whatever fits the battery settings. Series/parallel connections of panels are usually concerned with keeping input voltage within input limits of the controler and making sure you have sufficient voltage to initiate charging.

If you're only getting 170W there are a few causes:

Too little sun/panel shading

Resistance due to poor cabling/connections

Batteries too full to accept full charge

Wrong battery settings.

@Gsking

Basically power is volts multiplied by amps. W=V*A

15A x 12Volt (battery) is 180W

15A x 24V (battery) is 360W.

So yes if you are using a 24v battery you will be able to harvest more power with the 75\15 mppt.

If you are seeing less watts at 12v either you have less than 1000w/m² irradiation or your panels are above 25°C which is where they are rated.

No you cannot put more than 15A on the PV side. It will exceed the short circuit rating. See the tech specs

You need to look at VA, Volts X Amps, to get a handle on what is going on.

There could be many isues, and possibly none. The MPPT algorythan essentally varies amperage, by presenting different average loads, and tracks at what voltage and current the best power ia being achieved.

That 'point' will change significantly with the level of irradition and will be very different in full sun as opposed to defused light, cloud,mist and the like. It is also heavily influenced by the type and construction of the panels.

The silly number of variables is exactly why MPPT is not trying to be clever and predict the best voltage but is searching for it by making small changes and obsrving the results.

If your outpit is low, subjectivly, then something may be wrong but you should eliminate the simple stuff first... Connections, dirt, bad allignment, shading... and probably sveral more.

To do a reasonable comparison of the installation performance you need data from several periods that are 'broardly, the same, sun wise, before you could conclude that the MPPT is at fault.

Time and data will get you where ou need to be. I am not saying you dont have an issue, just that without dood data ou are unlikly to find it unless it is a simple obvious fault... Which I expect you have already checked for.

Lastly... If you are using a DC clamp to check current, make sure it will work at the switching frequency of he charge controller, many cant, or use data from the carage controller. The absplute accuracy isnt that importent just the consistency.

If you collect more data you will get better answers here... I am not in any critisizing, just ststing facts. When you have an issue, potential or real, data paints a picture and gets answers. without it all yu will get is guesses and generic advice. You clearly have a handle on the basics but you are probably looking for a nuanced issue.

I work in controls and systems intigration... After decades, I still think a day I dont learn something is a missed opertunity.

Info/Data is your friend, and likely your bigrest challange, when trying to pin down an odd behaviour.