Replace a combined landscape/architectural lighting transformer w/ Volt 300?

Have this old combined unit, looks like only about 7 wires coming into it, most of the unit is untapped. It's working fine but the company is out of business and the Grasslin timer no longer works. Annoyingly the Grasslin timer is enclosed and it looks like I need to take apart the entire enclosure to swap it out.

Thinking about just replacing the whole unit with a Volt 300 as I use one for the backyard already. The only thing that gives me pause is that the existing transformer also powers some of the architectural lighting out front.

If I count up the bulbs and I’m below the total wattage, am I good to go or will the 12-20 VAC architectural lighting really ding me? I assume I’d connect the architectural lights (think there's like two or three) to the Volts 15W connector in hopes it’ll be enough? Unfortunately it’s also the longest run.

Have no idea how much wattage the current unit is capable of.