And I disagree. You are just blowing unnecessary money when putting in synthetic, unless you are racing the car, or like I said, you prefer to keep your oil longer. As per the OP the manufacturer's customer service department said it's ok to put in regular oil, then just use regular oil, because it was designed for it.
Respectfully, I cannot disagree more. Case in point, the VW B5 era Passat 1.8 turbo history. Problems with oil sludging, cooked turbos, etc...Part of VW's solution was to mandate Synthetic Blend if not Full Synthetic, 502.00 VW spec. They would prefer you using Full Synthetic. And yes i have one of these exact cars. Did I run dino oil in it? YES FOR TWO CONSECUTIVE OIL CHANGES ONLY after I bought the car. Now I run nothing but full synthetic in it, period. If a 2000 VW turbo needs synthetic, now much more do today's turbo engines need it with closer tolerances, tighter engine compartments and higher intrinsic under-hood heat indexes?
Now, regarding the OP (Kodo_6GT's) comment here: "I read my owners manual it clearly states since my vehicle is a turbo application..the vehicle needs 5W30 synthetic engine oil. As a result, I immediately took the car to a different local dealer and this time they used 5W30 synthetic oil."
Keep in mind that my local Mazda dealership svc dept carries Castrol 5W-30 conventional oil. I have no idea if they also have synthetic, as this was before I had interest in a new Maz6 Siggy...
So I just downloaded the 2018 Owners manual. What I have found is this in section 6, pg 25:
Temperature Range SAE Viscosity Oils
Mazda Original Oil 5W-30 (this is a full synthetic)
Alternative Oil Quality:
API SN or ACEA A5/B5 0W-30 or 5W-30
API SN or ACEA A5/B5 10W-30, 5W-30, 0W-30
Just just where the OP found the Synthetic Specified in the manual remains in question, (unless they are in Europe and its clearly Recommended Synthetic)... having said that, though today's dino oils are better then ever (with additives for turbos, etc) today's synthetics are even BETTER. Add to that the old but still current adage:
"An ounce of Prevention prevents a pound of cure", I wouldn't skimp on motor oil on the cheap. Go all in and save yourself some massive cash outlay down the road on possible costly repairs that could have been avoided. It's not that much more $$ for the synthetic...what, the cost of one sub sandwich lunch?
Don't forget your spark plugs should be replaced every 60,000km (about 37,000 miles) on that 2.5T...