Thank you for your inputs and suggestions. In answer to one of the comments and to clarify, the 15,000kms which I mentioned pertains to the kilometrage after my last oil change kaya I know na sobrang overdue na sya.

Based on all your advice, and sa advice na din ng officemates ko, I'll bring my car (it's a Fortuner 2011 2.5G model) to the nearest gas station na today for to have the following changed: oil, oil filter and air filter. If they offer oil flush services, I'll avail na din. Medyo nagpanic ako sa mga feedback ng officemates ko when I told them about it. Sabi nung isa, baka daw pag chineck ung langis ko, burak na daw yun or worse, baka nagbuo buo na ung gunk sa loob. Kaya din I decided to go for the most expedient option, i.e. the nearest gas station.

Pag medyo maluwag ang sched ko and may extra budget na din, I'll bring it to the casa na din for a check up. Maraming salamat po sa lahat ng nagcomment. Your suggestions are all duly noted