Those who come up with 16 billion include Iranian people donation to reconstruct Shia shrines in Syria too which is mostly paid by people, they consider Iran annual salary for Shia fighter over 1.2 billion dollar while it's wrong it couldn't exceed more than 200 million $ and many other things ... As I said official estimation of Iran expenditure in Syria by UN is 6 billion $ which is roughly 10 % of Iran oil revenue while Iran has got other sources too (except 2013~2014 which this number was higher) ...
In total Iran has not spent more than 36~40 billion dollars in Syria.
On the other hand Qatar former FM said that Arab countries involved in bringing peace and security in Syria spent something around 137 billion dollars ..
The former Prime Minister of Qatar announced that a total of 137 billion dollars was wasted on the attempts to topple Assad’s government since the beginning of the war, while some of these funds were stolen by various field commanders that became millionaires overnight. In addition, considerable resources were wasted on the attempts to bribe Syria’s military brass, in attempt to persuade them in betraying their country or desert their positions. On average, a Syrian officer would receive from 15 to 30 thousand dollars for betraying his country.
The former Qatari official would announce that the ex-Prime Minister of Syria Riyad Farid Hijab was persuaded in fleeing Syria by his cousin, who had been a Jordanian resided for a long while. For this betrayal, Riyadh would pay him a handsome sum of 50 million dollars. In addition, the former commander of the Republican Guard Manaf Tlass would trade his home state for a chance to seek support of the UAR due to his sister’s successful attempts to persuade him into leaving. The sister, Madihi Tlass enjoyed French citizenship ever since she became the widow of the Syrian-Saudi businessman Akram Aja. This fact allowed French intelligence services to approach her to carry out the above mentioned operation.
Trump says the USA has spent 7 trillion $ in the region through invasion, occupation, CIA secret operations .. all these countries have poor people have economical problems for example only in the USA there are more than 40 million people whom don't know would they receive next meal or not , recent estimation shows employment ratio in Saudi Arabia getting to 12 percent while none of them face sanctions and has much more oil revenue.
Just last year Iranian spent 6.5 billion $ in Turkey and Georgia and Armenia (as far as I remember) for having fun ... some other went to Haj, our military expenditure is comparison by other expenditures is nothing even to the tiny countries of the southern part of Persian gulf in a way that many people in Iran are concern about our military strength .
Even if millions of Iranians suffer their daily life it ain't about our presence in Syria .. how it could be? albeit I prefer to spend less money for war and more for infrastructure, standing idle doing nothing regarding Iraq and Syria could have had dire repercussions for Iran and also entire region. but the point is we fought Saddam before any others (actually others were helping) as we fought Taliban before any others (actually others were helping) as we fought isis before any others (actually others were helping) and no one saw what we did .. the same happening in Syria too. we helped Iraqis in Arbil and Baghdad regardless being Sunni or Shia ..
What others want? secession of Iraq :
Just imagine the ethnical wars and conflicts these bastards seek to bring to the region ..
we helped Syrians to fight against terrorists while always insisted on diplomatic approach .. we helped people in Afghanistan more that 3.5 million Afghan people live in Iran as refugee and receive education job and other service just because of some idiots in Riyadh and Washington turned back the clock for the Afghan people .. many Iranian border guards have been martyred (more than 3.5k) in fight against opium smuggling other shiny example of American policy in the region ... and still we have Iran to blame.
The American bomb people in way that the ran out of bombing but who cares they have Hollywood and Media .. what Iran has? some stupid neighbors ...