Adobe AE render so slow [Beginner's question]

Hi. So I'm new to this field and have just built a PC with intention that I will learn to edit video in my free time. I suddenly got a request for help to render a video for my friend and decide it's a chance for me test my new system.

My specs: 

Intel Core I7-12700F

RTX 3060

32gb Corsair ram 3200ghz

SSD: Samsung 980 500TB

My friend's project: An 1-hr music video, with only one same background (a random photo) throughout the video, music (ofc), about 3 4 effects that are not supported by GPU accelaration.

Other settings include:

60fps, 1080p, H.264 codec, target bitrate: 15mbps

Render at maximum depth + maximum quality.

My question are:

Is it normal that I see my CPU not fully utilised all the time? In Task Manager, I see that it is 70 80%, sometimes 100% utilised but in other apps like iCUE or Intel Xt Tuning Utility, it's about only 40 50% utilised. GPU is also about 30 40%, sometimes 1 2% in as tracked in Task Manager. The RAM frequently stays at 17 - 23 and did reach it peak at 31.8gb in the end.

The system is not hot at all during the rendering process. Only about 50 - 60 degree Celcius. I can still did other works file during the rendering.

But the most important part is that at first it's shown that the rendering would take about 1.5hr, then gradually became 2, 3 and at its worst, nearly 8hrs and doesn't seem to reduce over the time at all.

I tried setting up as instructed on many places on the internet, such as allocate the RAM (29gb, maximum allowed) to AE and EN, turn on multi-frame rendering and such. Both the input files and output destination were also set to my SSD. 

Is it all normal? Has it always been that long and system-demanding to encode a 1080p, 60fps with only music and a few effects (i.e. snow, sound wave that move along the beats)? 

Thank you all in advance!